Conventionally, cBN sintered material cutting tools and the like, which have cutting tool bodies made of cBN sintered materials, are known as cutting tools for high hardness steel and various proposals have been made in order to improve their tool lives.
For example, Patent Literature 1 (PTL 1) discloses a cBN sintered material tool, in which reduction of the thermal conductivity of the tool body balances with improvement of the hardness of the tool body. In the cBN sintered material tool disclosed in PTL 1, the cBN sintered material includes cBN, the insulation phase, and the binder phase; cBN is included in the cBN sintered material from 60 volume % or more to less than 99 volume %; the insulation phase includes at least one or more of the first compound made of one or more elements selected from the group consisting of Al, Si, Ti and Zr and one or more elements selected from the group consisting of N, C, O, and B; the first compound is included in the cBN sintered material from 1 mass % or more to 20 mass % or less and has the average gran size of less than 100 nm; and the cBN sintered material has the thermal conductivity of 70 W/m·K or less.
In addition, Patent Literature 2 (PTL 2) discloses a cBN sintered material, in which fracturing resistance balances with abrasion resistance at a high level. In the cBN sintered material disclosed in PTL 2, the cBN sintered material includes cBN and the binder phase; the cBN is included in the cBN sintered material from 25 volume % or more to 80 volume % or less; the binder phase includes the Ti compound group; the Ti compound group includes one or more compounds containing at least Ti; the binder phase includes the first fine grain component constituted from grains having the grain size of 0.1 μm or less; and the first fine grain component occupies 10% to 60% of the area occupied by the binder phase at least in a cross-section of the cBN sintered material.
In addition, Patent Literature 3 (PTL 3) discloses a cBN sintered material, in which strength, toughness, and abrasion resistance are improved. In the cBN sintered material disclosed in PTL 3, the cBN sintered material includes: at least one selected from the group consisting of nitride, carbide, boride, oxide of the periodic table group 4a elements, the group 5a elements, the group 6a elements, and a solid solution thereof; at least one selected from the group consisting of an elemental substance of Zr, Si, Hf, Ge, W, and Co, a compound thereof, and a solid solution thereof; and an Al compound, as the bonding material. Furthermore, in the sintered material disclosed in PTL 3, the total content of W and/or Co is less than 0.5 weight %; the content of Si or Zr is 0.01 weight % or more and less than 0.5 weight %; Si/(Si+W+Co) or Zr/(Zr+W+Co) is 0.05 or more and 1.0 or less; the average grain size of TiN and TiB2, which are the Ti compound, is 100 nm or more and 400 nm or less; and the average grain size of AlB2 and AlN, which are the Al compound, is 50 nm or more and 150 nm or less.